Sebu and Koro-Sensei
by SparkFlameHero1
Summary: What if the God of Death had two students then one? What if there was more to they're teachers back story? What if there where... Two octopuses? But this one is blue and is ready for his soon to be Assassination Classroom. OC X OC, Nagisa X Harem


Assassination Classroom: Sebu & Koro-Sensei

 **Disclaimer: I don't own anything that is of Assassination Classroom, but my OC's. And let's give thanks to the one that inspired me. Thank you, PainX65.** **Please support and read his fan fictions. Now enjoy and leave a comment on what you think.**

Chapter 1: Assassination Time!

Many of strange things have happen lately. Like the day 70% of the moon was destroyed. Who did it and why is unknown. But the answers lie in a class known as Class 3-E at Kunugigaoka Junior High as their homeroom teacher comes to start class.

"Alright then class, shall we get started? Class monitor would you please?" the yellow octopus teacher asked the blue haired student.

"Right!" he said then every student got up and each was holding a firearm.

"Ready! Aim! Fire!" And so they did. Round after round they shot at the octopus with pink pellets known as anti-sensei bullets.

But, to no prevail as the yellow creature dodged every shot with his mach 20 speed.

"Oh, my, well, as you take a shot at me I'll take attendance." he said as he looked at his book with each student's name.

"Isogai?" E-2 Yuma Isogai, he has spiked brown hair with two small hair antennae at the top of his head and pale gold eyes. In addition to his personality, Yuma has been described as being very attractive and is one of the most popular members of Class 3-E. He's also popular with others from the main building and still receives love letters from females there despite the otherwise general discrimination. -.-….. In other words he's a 'Prince Charming.' (No offense, but I really hate those types. I mean it's like what do women see in them when we don't? ...Anyway moving on.)

"Here!"

"Sorry, we're in gunfire could you speak up a little please?"

"HERE!"

"Okajima?" E-3 Taiga Okajima, he has short, black hair in a butch cut and thick eyebrows. Okajima is the class pervert and is rather open about it. He is also known for peeping and reading erotica magazines.

"HERE!"

"Okano?" E-4 Hinata Okano, she has short brown hair and light purple eyes and her hair is the shortest among all the girls in Class 3-E. In her initial appearance, Okano is often shown to be serious with a relatively neutral expression.

"HERE!"

"Okuda?" E-5 Manami Okuda, she has black hair, styled into twin braids that reach just below her shoulders and lavender eyes. She wears glasses and has a more petite frame than most of the girls in Class 3-E. Okuda is a shy and rather introverted girl. She has poor language skills and is straightforward because of it. Despite her introversion, she's a sweet and determined girl who hopes to be useful to the class.

"HERE!"

"Kataoka?" E-6 Megu Kataoka, Kataoka is a tall girl with long, gray hair kept in a ponytail with straight bangs. She is described as being "dashing". She also has the physique and making of a model.

"HERE!"

"Kayano?" E-7 Kaede Kayano, Kayano is a girl with a short stature. She has a little frame, hazel eyes, and green hair which are always fashioned in unique, cat ear-styled pigtails. A running gag for her appearance is that she is "forever flat", referring to her not having noticeable breasts like the other female students in the class. (Spoiler: And she later on has a crush on a certain blue haired boy. Try and guess... oh, you know already.)

"HERE!"

"Kanzaki?" E-8 Yukiko Kanzaki, Yukiko has long, straight black hair and light brown eyes. She is noted for being very beautiful by everyone in Class E, and is one of the reasons why she's the most popular girl in Class E.

"HERE!"

"Kimura?" E-9 Masayoshi Kimura, Kimura is one of the relatively proactive students. He hates his own name because people would pick on him because of said name means 'Justice'.

"HERE!"

"Kurahashi?" E-10 Hinano Kurahashi, she has short, wavy orange hair and peridot green eyes. She has more petite frame than most of the girls in Class 3-E. She is an energetic and positive girl and is always seen with a smile on her face regardless of the situation.

"HERE!"

"Shiota-kun?" E-11 Nagisa Shiota, Nagisa is a petite framed boy with light blue hair and azure eyes. His hair would normally go past his shoulders due to his mother forcing him to keep it that way. When he met a certain 'green haired girl' he now keeps his hair in two pigtails. He is known for his androgynous appearance which has often been poked fun at by many other people. (Main character, *cough* *cough*, leader of class, best out of the entire class. *Cough*.)

"HERE!"

"Sugaya?" E-12 Sosuke Sugaya, Sosuke is a tall and slender male with dark grey/silver hair that goes past his ears and dark eyes. He is a well-meaning and easy-going person who's also very creative. He has a love and talent for art and has a calm demeanour.

"HERE!"

"Sugino?" E-13 Tomohito Sugino, he has the generic short, spiked black hair for male shonen character and dark blue eyes. Out of all the males in his class, he is the most normal. Sugino is an energetic boy with a love for baseball. He's a very happy and friendly person and gets along with his classmates well.

"HERE!"

"Takebayashi?" E-14 Kotaro Takebayashi, Takebayashi has black hair combed over along the sides of his head and wears round eyeglasses. His uniform consists of a suit jacket worn over a dress shirt and a black tie, as well as dress pants and dress shoes. Takebayashi is mostly a quiet person. However, he seems somewhat eccentric in his behavior and stands out as the oddball in the class. He also seems to be clumsy at physical activity. He is also obsessed with anime, at one point stating "A girl isn't a true girl until she loses the third D" implying he likes anime girls more than real women. He also enjoys going to maid cafes.

"HERE!"

"Chiba?" E-15 Ryunosuke Chiba, Ryūnosuke has black hair with long bangs that cover his eyes. It is revealed that his bangs mark off part of his vision. And it happens that he has reddish-brown eyes under his hair. Chiba is a serious and stoic boy. He's very calm and business like and doesn't talk a lot.

"HERE!"

"Terasaka?" E-16 Ryoma Terasaka, Terasaka has short, spiky, black hair which is dyed blonde around the sides. He has a bulky body which he uses to intimidate people with and green eyes. Terasaka is a former bully who enjoyed picking on people because of his large build and loud voice. He is rather dim-witted and relies on others to make plans for him to follow which makes it very easy for others to manipulate him. In addition he is also quick to anger and is very lazy which is why he's in Class E.

"HERE!"

"Nakamura?" E-17 Rio Nakamura, Rio has long, straight blonde hair and blue eyes. Rio is a friendly, energetic girl and somewhat of a trickster. She's playful, has a bit of a dirty mind, and has been noted to be rather intelligent. She claims she was originally a serious person.

"HERE!"

"Hazama?" E-18 Kirara Hazama, Hazama is a slender girl with messy, shoulder-length black hair and thick eyelashes. As such, she comes off as very gloomy and melancholic. She believes part of the reason she looks the way she does is due to her mother being prone to screaming fits thus preventing her from looking cute like her given name. (May I also include that she scares me.)

"HERE!"

"Hayami?" E-19 Rinka Hayami, Rinka has medium-length wavy orange-brown hair and green eyes. In her early appearance she wore her hair down, but now she began wearing them in low pigtails. She's very stoic, businesslike, and professional and has been compared to a working adult along with Chiba. She's quiet and calm and has been shown to be straight-forward.

"HERE!"

"Hara?" E-20 Sumire Hara, Somewhat large body with hair usually tied into a pony-tail. Hara is one of the more passive members of the class. She is usually regarded as a motherly figure, due to her ability to cook and care for the class. She has shown offense when people call her heavy.

"HERE!"

"Fuwa?" E-21 Yuzuki Fuwa, Yuzuki has short dull brown hair with straight bangs and light purple eyes. Fuwa has an imaginative and enthusiastic personality. She is a manga fan, particularly of the shōnen demographic as evidenced with her commonly referencing, mentioning, or reading Weekly Shōnen Jump and other shōnen magazines.

"HERE!"

"Maehara?" E-22 Hiroto Maehara, Hiroto is fairly tall for a middle school student. He has wavy mid-short, orange-brown hair and eyes. He has been noted to be very good-looking. Maehara is a nice guy and in every sense of the word, a playboy. He has a "live the moment" attitude about life in general. He is one of the few that is popular in the whole school despite being in the E Class. Despite that attitude, he is a caring person and isn't the type to pick on someone weaker than him. He's also an honest type of guy, and often reacts strongly to things.

"HERE!"

"Mimura?" E-23 Koki Mimura, Mimura has orange-brown hair styled in bowl cut and green eyes. He's noted for having a plain appearance. Possibly one of the more "normal" students in the class, Mimura is a relatively plain boy with seemingly no special skills outside of directing. He's a friendly guy who originally had little to no confidence in himself like the rest of the class.

"HERE!"

"Muramatsu?" E-24 Takuya Muramatsu, Takuya is one of the more independent members of the class, staging assassinations at his own pace. Takuya's family runs the Ramen Shop "Matsuraiken". Takuya would often try to persuade his father without success to change his recipe as the ramen he makes is too bland.

"HERE!"

"Yada?" E-25 Toka Yada, Yada has mid-brown hair held up in a ponytail and presumably light purple eyes. She also has the largest bust out of all the female students in Class E. She is the big sister of Class 3-E and one of the most enthusiastic students and she's been described as being adult-like and cool.

"HERE!"

"And last but not least, Yoshida?" E-26 Taisei Yoshida, Yoshida is one of the more independent members of the class, Like Muramatsu. Due to being the son of a motorcycle company owner, Yoshida is very good with mechanics and engineering; more specifically, vehicle engineering.

"HERE!"

As he marked the last name all the students stop shooting. Not only from being tired, but that they didn't even hit him.

"Alrighty then, no tardies, and this makes sensei very pleased." he said as a red circle appeared on his face.

"He's way too fast." Rio said.

"Even with the whole class shooting at him it didn't work." Yuma said with a frown.

'We are assassins. Our target is our teacher.' Nagisa thought to him self. (Think he's narrating the story? Sorry folks, but that's my job.)

"Not a single hit today. Too bad." the octopus said without a care in the world. "Today, you learn that it's not all about numbers. Anyone can bring a gun and shoot, but your idea lacked creativity."

"When your target moves at mach 20 you need to think outside the box." he explained.

"There's no way you dodge all of those!" Hiroto complained.

"He's got a point. These are just BB pellets. For all we know you probably just stood there and took them all head on." Tomohito agreed.

Their teacher sighed at their complaining. "Collect all the BBs and hand them over." he said as he took a gun from Hinata.

"As I said before: these BBs maybe harmless to you and others..." he then shot one of his tentacles off like it was a hot knife through butter.

This got everyone's attention. "...these are anti-sensei BBs or Anti-me BBs as I like to call them, were developed by the government. With just one shot can rip through me like butter. But, don't worry. My tentacles regenerate in seconds. Something you can't do if you shoot your eye out." he explained as his tentacle grew back.

"Now put your guns away now." He said as his grin grew with green strips appeared on his face. "And good luck to killing me till graduation. You're going to need it. Nurufufufufu…"

Outside the building, waiting a few miles away hidden in a tree deep in the forest was a figure. "So this is Class 3-E, or known as the Assassination Classroom." A man in his 20's said as he looked over a roll book of all the students.

"All these students have potential. Especially this one." he stopped his finger on a picture of Nagisa.

"It seems class is starting. Lets see what you have Students of Class 3-E."

As class went on the lunch bell rang and their teacher left to get his own lunch and said he'll be back soon.

Then Ryoma and his friends went to talk to Nagisa about a plan to kill their teacher.

"Ryoma, from what I heard is a bully and not as smart from others." The man from the woods said to himself. "I'll give him an 'A' for effort from going to Nagisa for help since he is the only one keeping track of his targets weakness." he continued to listen on the conversation.

As Ryoma and his friends left, Nagisa was left by himself thinking.

"You know, if I were you I wouldn't go through with it." Nagisa turned to see a strange man standing next to him. He had short brown hair and dark brown eyes. He had to be 5.11ft tall, wearing a white long sleeve button up shirt with a shark fin 'O' on his right pocket. And he was wearing regular black pants and shoes.

"Where did you come from?" All the man did was chuckle.

"My name is Orlando. You must be Nagisa of 3-E am I right?" he asked.

"Yeah that's right."

"Well, if you're gonna kill your teacher you're gonna take his advice and think outside the box kid. Ryoma's plan might get you hurt or even worse kid."

"Wait, how did you know..." then he was gone. No trace of him to be found.

Then right then the teacher of the hour landed on the ground with a missile.

"Hello Nagisa, I'm back!" he said with his smile.

"Hello sir. What's with the missile?" he asked.

"Oh, this little thing…? I got it when a strike force tried to strike me down over the sea of Japan." he explained.

"It must be hard when you're a target."

"Quiet the opposite, actually. Reminds me of how amazing I am!" he boasted about himself. "Now its time for fifth period." he said as he was making his way to the building.

"Wait um, sir."

"Yes?"

"Before you came did you see someone here by any chance?" Nagisa asked.

"Why no, is there someone else here trying to do me in?"

"No, I guess it was my imagination." Nagisa chuckled and went inside with his teacher.

"We'll kid, let's see if you can pull this off." Orlando said as he continued to watch.

Then class continued as everyone was seated.

"Okay class, now today's assignment is a short poem. The final line should read, "it was tentacles all along." he said.

"Excuse me sir, but really?"

"Really, and when you finish your assignment kindly bring it to me please. You'll be graded on creativity, grammar, and over all the beauty of expression." he said. "For example, "Not the storm of garden snow of flowers moving on but sprouting there it was tentacles all along." he stated.

"Yeah like that makes a whole lot of sense."

"You may go home once you're finished."

"W-what…? B-But sir…"

"I'm sure this will get those imaginations of yours going like my tentacles." he giggled as he wiggled his tentacles.

"Um, sir question!" Kayano asked with her hand up.

"Of course, fire away Kayano."

"Do we always have to call you sir? You haven't given us your name, I think we need one. I mean it would be kind of awkward if we don't call you anything right?" she said.

"Ah, well now..."

"Oversight…"

"Yeah a little bit."

"Hmmm, trouble is I don't have the sort of name you just give to people. Why not pick one for me?" he said.

"What could go wrong?"

"Just focus on reading and syntax."

"Ok!"

"Now, I'll take a short break while you take up your pens." his color then changed to pink as he seemed that he needed to relax.

With that Nagisa got up from his desk and walked slowly to his teacher.

"Seem the muse favors Nagisa." the teacher looked up but didn't change color.

As Nagisa was making his way he started making his point about his teachers weakness.

'His face turns pink means he's checked out meaning he's sleepy. This should be the right moment.' he continued to think about himself and his classmates. Being the lowest of the low gives them an advantage of cracks like this.

As he made it to the teacher, he tried to strike the octopus with an anti-senesi knife. Only to fail as said teacher easily caught Nagisa's wrist.

"What did I say about thinking outside the box?" he said as he removed the blade with a tissue.

But as this was going on Nagisa went in for the kill as he got his teacher in an embrace as well with a grenade around his neck, but with a smile on his face as Ryoma press a button as it exploded in their teacher's face.

But as Ryoma thought he killed him, Nagisa was ok. Not a scratch on him as he was covered with a weird layer of skin.

"Don't go thinking it's a body it's a husk. I shed my skin once a month. I wrapped it around your classmate so he wouldn't get hurt from the blast." they soon found their teacher clanging to the ceiling with red eyes and his color changing to pure black.

'I'm guessing that black is, pissed off.' Nagisa thought.

"Oh, now they've done it." Orlando said from outside. A few meters away.

The teacher then left and came back in a flash with the name plates of his student's houses.

"The deal I had with your government was that I'm forbidden to harm you. But, there's a catch if you pull another irresponsible stunt like that again, there's nothing stopping me to hurt someone else. Family, Friends, everyone in the world except for you if I feel like it!" he explained with a dangerous tone.

'We can't run or hide. Our only choice is to kill him.' Nagisa thought.

"Go on threaten us! I'm not afraid of no squid! Where do you get off blowing up the moon? We got rights! Call us what you want we're just defending ourselves!" Ryoma said in fear.

Then their teacher's face change bright red with a circle.

"Of course I know that. I'm not calling you irresponsible for trying to kill me!" he said as he put a feeler on Nagisa's head. "No, no, no, as a matter of fact Nagisa here gets full marks for technique. His composure was simply marvellous." he praised his student then he glared as he pointed a feeler at Ryoma and his friends.

"However, none of you cared for his safety. Not even Nagisa himself it seems. Students with that attitude aren't fit to assassinate anyone!" he then changed to purple with an x on his face.

"You must believe yourself worthy of your target. That means taking pride in what you do. Me, you and each other my dear students." he said as he looked at his class.

"All of you are more than the sum of your parts."

"Heh, I'll give it to him. The kid got what it takes." Orlando said as he continued to look with a cheeky grin.

"Here's a puzzler for you Nagisa. Given the fact I have no intention to being killed, though of course I have every intention of enjoying our time together before the planet goes bang and kaplooey, what exactly are you going to do about it my boy?" he asked.

Nagisa thought for a moment then he smiled. "I think you'll find out I can do plenty sir. Just you wait and see."

"Nufufufufu!" the octopus laughed as he had green strips on his face. "That's the spirit. No leaves till I'm vanquished!" he said making everyone groan and Nagisa returned to his seat.

"Hey, how do you say unkillable in Japanese?" Kayano asked as she tried to figure it out. "Korosenmi? Ah! Koro-Sensei!"

And so it was decided. Their teacher was known from this day forth as: Koro-Sensei.

"Heh… Koro-Sensei huh, seems fitting. Eh, guess its time." Orlando said to himself.

He soon disappeared in a few short seconds. Deep in the woods was a two story house hidden from anyone from the outside.

Orlando made it in and smiled to a woman pouring herself a cup of tea.

"I'm guessing it went well?" she asked.

"Better than expected my dear. They even gave him a name. They call him Koro-Sensei." he explained as he poured his own cup.

"I see. It suits him well. I'm sure they will find it hard to kill him. Though, what if it was you in his place? As a target?" she asked taking a sip.

He just stood there as his limbs changed, turning into blue tentacles. He then changed his clothes similar to Koro-Sensei's, but his tie had both the sun and the crescent moon. His smile was normal, but then changed to a grin as green strips surrounded his face.

"Nufufufufufu! If it were me my dear." he laughed. "I think it will take them more then a year to kill me then my master."

 **I hoped you all enjoyed this. As said before give thanks to PainX65. He also beta this for me so I'm greatful to him for his help. Anyway, who is this mysterious man? How is he able to change shape? How does he know of the assassination classroom and Korosensei? And who is this women he was talk to? Your gonna have to continue reading and find out. Nufufufufufu! SparkFlames out!**


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